Thanks for the replies and suggestions............ The grille I am trying to repair is an NOS GM grille I bought that was damaged during shipping. This is what I have tried so far. I have been cutting test pieces out my old beat up grille that the NOS one is replacing and tyring different adhesives. I make sure the mating surfaces are clean and sanded................I have tried ABS plastic pipe glue, Testors model airplane glue, Loctite super glue, regular JB Weld, and JB Plastic Weld. I have some Gorilla epoxy curing now. With each, I have glued two flat pieces together and then tried to pry them apart after they are cured. The ABS pipe glue, Testors, Loctite, and regular JB Weld all failed pretty easily. The strongest bond was the JB Plastic Weld. It was more difficult to split apart than all the others and it was the Plastic Weld itself that broke apart. It's bond to the pieces of the grille did not not break where all of the others did.

I was hoping one of these would melt the plastic together or bond strong enough where the plastic would break before the adhesive.

I also tried melting with a soldering iron but the soldering iron I have doesn't seem to get hot enough to really make the plastic flow.

It seems from what I read that you really need to know what kind of plastic you are dealing with in order to find the correct adhesive. There are some plastic adhesives that say they won't work on polyethylene or polypropylene plastics.....Does anyone know for sure what these '68 center grilles are made of ?